Planetary gear train of automatic transmission for vehicle

ABSTRACT

A planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting changed torque of the engine, a first planetary gear set including a first rotation element, a second rotation element, and a third rotation element, a second planetary gear set including a fourth rotation element, a fifth rotation element, and a sixth rotation element, a third planetary gear set including a seventh rotation element, an eighth rotation element, and a ninth rotation element, and a fourth planetary gear set including a tenth rotation element, an eleventh rotation element, and a twelfth rotation element.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2015-0176322, filed Dec. 10, 2015, the entire contents of which isincorporated herein for all purposes by this by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an automatic transmission for avehicle. More particularly, the present invention relates to a planetarygear train of an automatic transmission for a vehicle that improvespower delivery performance and fuel economy by achieving at least nineforward speed stages and widening speed ratio (or gear ratio) with aminimum number of constituent elements being used, and secures linearityof step ratios.

Description of Related Art

Recent increases in oil prices are triggering stiff competition amongauto-makers in enhancing fuel consumption of a vehicle.

Such an automatic transmission achieving more speed stages is necessaryto maximize power performance and driving efficiency according todownsizing of an engine. Particularly, it is desperately needed todevelop high efficiency multiple-speed stage transmissions havingexcellent linearity of step ratios that can be used as an index closelyrelated to drivability such as acceleration before and after shift, andrhythmical engine speed in order to secure competitiveness of automatictransmission field.

However, in the automatic transmission, as the number of speed stagesincrease, the number of internal components increase, and as a result,mountability, cost, weight, transmission efficiency, and the like maystill deteriorate.

Accordingly, development of a planetary gear train which may achievemaximum efficiency with a small number of components is important inorder to increase a fuel efficiency enhancement effect through themultiple-speeds.

In this aspect, in recent years, 8-speed automatic transmissions tend tobe implemented and the research and development of a planetary geartrain capable of implementing more speed stages has also been activelyconducted.

However, since a conventional 8-speed automatic transmission has a gearratio span of 6.5-7.5 (gear ratio span is an important factor forsecuring linearity of step ratios), improvement of power performance andfuel economy may not be great.

In addition, if an 8-speed automatic transmission has gear ratio spanlarger than 9.0, it is hard to secure linearity of step ratios.Therefore, driving efficiency of an engine and drivability of a vehiclemay be deteriorated, and thus, development of high efficiency automatictransmissions which achieve at least nine forward speed stages isnecessary.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing aplanetary gear train of an automatic transmission for a vehicle havingadvantages of improving power delivery performance and fuel economy byachieving nine forward speed stages and one reverse speed stage, andwidening gear ratio span and of securing linearity of step ratios.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, and afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, in which the input shaft may be directly connected tothe second rotation element, the output shaft may be directly connectedto the eleventh rotation element, the first rotation element maydirectly connect the sixth rotation element with the tenth rotationelement, the second rotation element may be directly connected to thefourth rotation element, the fifth rotation element may be directlyconnected to the ninth rotation element, and the seventh rotationelement may be selectively connectable to a transmission housing.

The eighth rotation element may be selectively connectable to thetransmission housing, the twelfth rotation element may be selectivelyconnectable to the transmission housing, the third rotation element maybe selectively connectable to the eleventh rotation element, the eighthrotation element may be selectively connectable to the input shaft, andthe first rotation element may be selectively connectable to the eighthrotation element.

The first, second, and third rotation elements may be a first sun gear,a first planet carrier, and a first ring gear, the fourth, fifth, andsixth rotation elements may be a second sun gear, a second ring gear,and a second planet carrier, the seventh, eighth, and ninth rotationelements may be a third sun gear, a third planet carrier, and a thirdring gear, and the tenth, eleventh, and twelfth rotation elements may bea fourth sun gear, a fourth planet carrier, and a fourth ring gear.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, a first rotation shaft directly connecting the firstrotation element with the sixth rotation element and the tenth rotationelement, a second rotation shaft directly connecting the second rotationelement with the fourth rotation element and directly connected to theinput shaft, a third rotation shaft directly connected to the thirdrotation element, a fourth rotation shaft directly connecting the fifthrotation element with the ninth rotation element, a fifth rotation shaftdirectly connected to the seventh rotation element and selectivelyconnectable to a transmission housing, a sixth rotation shaft directlyconnected to the eighth rotation element, selectively connectable to atleast one of the first rotation shaft and the second rotation shaft, andselectively connectable to the transmission housing, a seventh rotationshaft directly connected to the eleventh rotation element, selectivelyconnectable to the third rotation shaft, and directly connected to theoutput shaft, and an eighth rotation shaft directly connected to thetwelfth rotation element and selectively connectable to the transmissionhousing.

The first planetary gear set may be a single pinion planetary gear set,the first rotation element may be a first sun gear, the second rotationelement may be a first planet carrier, and the third rotation elementmay be a first ring gear, the second planetary gear set may be a doublepinion planetary gear set, the fourth rotation element may be a secondsun gear, the fifth rotation element may be a second ring gear, and thesixth rotation element may be a second planet carrier, the thirdplanetary gear set may be a single pinion planetary gear set, theseventh rotation element may be a third sun gear, the eighth rotationelement may be a third planet carrier, and the ninth rotation elementmay be a third ring gear, and the fourth planetary gear set may be asingle pinion planetary gear set, the tenth rotation element may be afourth sun gear, the eleventh rotation element may be a fourth planetcarrier, and the twelfth rotation element may be a fourth ring gear.

The planetary gear train may further include a first clutch selectivelyconnecting the third rotation shaft with the seventh rotation shaft, asecond clutch selectively connecting the second rotation shaft with thesixth rotation shaft, a third clutch selectively connecting the firstrotation shaft with the sixth rotation shaft, a first brake selectivelyconnecting the sixth rotation shaft with the transmission housing, asecond brake selectively connecting the fifth rotation shaft with thetransmission housing, and a third brake selectively connecting theeighth rotation shaft with the transmission housing.

A first forward speed stage may be achieved by operation of the thirdclutch and the first and third brakes, a second forward speed stage maybe achieved by operation of the second and third clutches and the thirdbrake, a third forward speed stage may be achieved by operation of thesecond clutch and the first and third brakes, a fourth forward speedstage may be achieved by operation of the first clutch and the first andthird brakes, a fifth forward speed stage may be achieved by operationof the first and second clutches and the first brake, a sixth forwardspeed stage may be achieved by operation of the first, second, and thirdclutches, a seventh forward speed stage may be achieved by operation ofthe first and third clutches and the first brake, an eighth forwardspeed stage may be achieved by operation of the first and third clutchesand the second brake, a ninth forward speed stage may be achieved byoperation of the first clutch and the first and second brakes, and areverse speed stage may be achieved by operation of the first, second,and third brakes.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque, a first planetary gear set comprising a single pinion planetarygear set and including first, second, and third rotation elements, asecond planetary gear set comprising a double pinion planetary gear setand including fourth, fifth, and sixth rotation elements, a thirdplanetary gear set comprising a single pinion planetary gear set andincluding seventh, eighth, and ninth rotation elements, a fourthplanetary gear set comprising a single pinion planetary gear set andincluding tenth, eleventh, and twelfth rotation elements, a firstrotation shaft directly connecting the first rotation element with thesixth rotation element and the tenth rotation element, a second rotationshaft directly connecting the second rotation element with the fourthrotation element and directly connected to the input shaft, a thirdrotation shaft directly connected to the third rotation element, afourth rotation shaft directly connecting the fifth rotation elementwith the ninth rotation element, a fifth rotation shaft directlyconnected to the seventh rotation element and selectively connectable toa transmission housing, a sixth rotation shaft directly connected to theeighth rotation element, selectively connectable to at least one of thefirst rotation shaft and the second rotation shaft, and selectivelyconnectable to the transmission housing, a seventh rotation shaftdirectly connected to the eleventh rotation element, selectivelyconnectable to the third rotation shaft, and directly connected to theoutput shaft, an eighth rotation shaft directly connected to the twelfthrotation element and selectively connectable to the transmissionhousing, a first clutch selectively connecting the third rotation shaftwith the seventh rotation shaft, a second clutch selectively connectingthe second rotation shaft with the sixth rotation shaft, a third clutchselectively connecting the first rotation shaft with the sixth rotationshaft, a first brake selectively connecting the sixth rotation shaftwith the transmission housing, a second brake selectively connecting thefifth rotation shaft with the transmission housing, and a third brakeselectively connecting the eighth rotation shaft with the transmissionhousing. Various embodiments of the present invention achieve at leastnine forward speed stages and one reverse speed stage by combining fourplanetary gear sets being simple planetary gear sets with six controlelements.

In addition, since gear ratio span greater than 9.0 is secured, drivingefficiency of the engine is maximized.

Furthermore, since linearity of step ratios is secured due to multiplespeed stages, drivability such as acceleration before and after shift,rhythmical engine speed, and so on are improved.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g., fuel derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example, bothgasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a planetary gear train according tovarious embodiments of the present invention.

FIG. 2 is an operation chart of control elements at each speed stage inthe planetary gear train according to various embodiments of the presentinvention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

FIG. 1 is a schematic diagram of a planetary gear train according tovarious embodiments of the present invention.

Referring to FIG. 1, a planetary gear train according to variousembodiments of the present invention includes first, second, third, andfourth planetary gear sets PG1, PG2, PG3, and PG4 disposed on the sameaxis, an input shaft IS, an output shaft OS, eight shafts TM1 to TM8connected to at least one of rotation elements of the first, second,third, and fourth planetary gear sets PG1, PG2, PG3, and PG4, sixcontrol elements C1 to C3 and B1 to B3, and a transmission housing H.

Torque input from the input shaft IS is changed by cooperation of thefirst, second, third, and fourth planetary gear sets PG1, PG2, PG3, andPG4, and the changed torque is output through the output shaft OS.

The planetary gear sets are disposed in a sequence of the first, second,third, and fourth planetary gear sets PG1, PG2, PG3, and PG4 from anengine.

The input shaft IS is an input member and the torque from a crankshaftof an engine, after being torque-converted through a torque converter,is input into the input shaft IS.

The output shaft OS is an output member, is disposed in parallel withthe input shaft IS, and transmits driving torque to a driving wheelthrough a differential apparatus.

The first planetary gear set PG1 is a single pinion planetary gear setand includes a first sun gear S1, a first planet carrier PC1 rotatablysupporting a first pinion P1 that is externally meshed with the firstsun gear S1, and a first ring gear R1 that is internally meshed with thefirst pinion P1 respectively as first, second, and third rotationelements N1, N2, and N3.

The second planetary gear set PG2 is a double pinion planetary gear setand includes a second sun gear S2, a second ring gear R2 internallymeshed with a second pinion gear P2 externally meshed with the secondsun gear S2, and a second planet carrier PC2 rotatably supporting thesecond pinion gear P2 as fourth, fifth, and sixth rotation elements N4,N5, and N6.

The third planetary gear set PG3 is a single pinion planetary gear setand includes a third sun gear S3, a third planet carrier PC3 rotatablysupporting a third pinion P3 that is externally meshed with the thirdsun gear S3, and a third ring gear R3 that is internally meshed with thethird pinion P3 respectively as seventh, eighth, and ninth rotationelements N7, N8, and N9.

The first rotation element N1 is directly connected to the sixthrotation element N6 and the tenth rotation element N10, the secondrotation element N2 is directly connected to the fourth rotation elementN4, and the fifth rotation element N5 is directly connected to the ninthrotation element N9 such that the first, second, third, and fourthplanetary gear sets PG1, PG2, PG3, and PG4 include eight rotation shaftsTM1 to TM8.

The eight shafts TM1 to TM8 will be described in further detail.

The first rotation shaft TM1 directly connects the first rotationelement N1 (first sun gear S1) with the sixth rotation element N6(second planet carrier PC2) and the tenth rotation element N10 (fourthsun gear S4).

The second rotation shaft TM2 directly connects the second rotationelement N2 (first planet carrier PC1) with the fourth rotation elementN4 (second sun gear S2) and is directly connected to the input shaft ISso as to be operated as an input element continuously.

The third rotation shaft TM3 is directly connected to the third rotationelement N3 (first ring gear R1).

The fourth rotation shaft TM4 directly connects the fifth rotationelement N5 (second ring gear R2) with the ninth rotation element N9(third ring gear R3).

The fifth rotation shaft TM5 is directly connected to the seventhrotation element N7 (third sun gear S3) and is selectively connectableto the transmission housing H so as to be operated as a selective fixedelement.

The sixth rotation shaft TM6 is directly connected to the eighthrotation element N8 (third planet carrier PC3), is selectivelyconnectable to the first rotation shaft TM1 or the second rotation shaftTM2, and is selectively connectable to the transmission housing H so asto be operated as a selective fixed element.

The seventh rotation shaft TM7 is directly connected to the eleventhrotation element N11 (fourth planet carrier PC4), is selectivelyconnectable to the third rotation shaft TM3, and is directly connectedto the output shaft OS so as to be continuously operated as an outputelement.

The eighth rotation shaft TM8 is directly connected to the twelfthrotation element N12 (fourth ring gear R4) and is selectivelyconnectable to the transmission housing H so as to be operated as aselective fixed element.

In addition, three clutches C1, C2, and C3 that are control elements aredisposed at portions at which two rotation shafts among the rotationshafts TM1 to TM8 are selectively connectable to each other.

In addition, three brakes B1, B2, and B3 that are control elements aredisposed at portions at which any one rotation shaft among the rotationshafts TM1 to TM8 is selectively connectable to the transmission housingH.

Arrangements of the six control elements C1 to C3 and B1 to B3 aredescribed in detail.

The first clutch C1 is disposed between the third rotation shaft TM3 andthe seventh rotation shaft TM7 and selectively connects the thirdrotation shaft TM3 with the seventh rotation shaft TM7.

The second clutch C2 is disposed between the second rotation shaft TM2and the sixth rotation shaft TM6 and selectively connects the secondrotation shaft TM2 with the sixth rotation shaft TM6.

The third clutch C3 is disposed between the first rotation shaft TM1 andthe sixth rotation shaft TM6 and selectively connects the first rotationshaft TM1 with the sixth rotation shaft TM6.

The first brake B1 is disposed between the sixth rotation shaft TM6 andthe transmission housing H and causes the sixth rotation shaft TM6 to beoperated as a selective fixed element.

The second brake B2 is disposed between the fifth rotation shaft TM5 andthe transmission housing H and causes the fifth rotation shaft TM5 to beoperated as a selective fixed element.

The third brake B3 is disposed between the eighth rotation shaft TM8 andthe transmission housing H and causes the eighth rotation shaft TM8 tobe operated as a selective fixed element.

The control elements including the first, second, and third clutches C1,C2, and C3 and the first, second, and third brakes B1, B2, and B3 may bemulti-plates friction elements of wet type that are operated byhydraulic pressure.

FIG. 2 is an operation chart of control elements at each speed stage inthe planetary gear train according to various embodiments of the presentinvention.

As shown in FIG. 2, three control elements are operated at each speedstage in the planetary gear train according to the various embodimentsof the present invention.

The third clutch C3 and the first and third brakes B1 and B3 areoperated at a first forward speed stage D1.

In a state that the first rotation shaft TM1 is connected to the sixthrotation shaft TM6 by operation of the third clutch C3, torque of theinput shaft IS is input to the second rotation shaft TM2. In addition,the sixth and eighth rotation shafts TM6 and TM8 are operated as thefixed elements by operation of the first and third brakes B1 and B3.Therefore, the torque of the input shaft IS is shifted into the firstforward speed stage, and the first forward speed stage is output throughthe output shaft OS connected to the seventh rotation shaft TM7.

The second and third clutches C2 and C3 and the third brake B3 areoperated at a second forward speed stage D2.

In a state that the second rotation shaft TM2 is connected to the sixthrotation shaft TM6 by operation of the second clutch C2 and the firstrotation shaft TM1 is connected to the sixth rotation shaft TM6 byoperation of the third clutch C3, the torque of the input shaft IS isinput to the second rotation shaft TM2. In addition, the eighth rotationshaft TM8 is operated as the fixed element by operation of the thirdbrake B3. Therefore, the torque of the input shaft IS is shifted intothe second forward speed stage, and the second forward speed stage isoutput through the output shaft OS connected to the seventh rotationshaft TM7.

The second clutch C2 and the first and third brakes B1 and B3 areoperated at a third forward speed stage D3.

In a state that the second rotation shaft TM2 is connected to the sixthrotation shaft TM6 by operation of the second clutch C2, the torque ofthe input shaft IS is input to the second rotation shaft TM2. Inaddition the sixth and eighth rotation shafts TM6 and TM8 are operatedas the fixed elements by operation of the first and third brakes B1 andB3. Therefore, the torque of the input shaft IS is shifted into thethird forward speed stage, and the third forward speed stage is outputthrough the output shaft OS connected to the seventh rotation shaft TM7.

The first clutch C1 and the first and third brakes B1 and B3 areoperated at a fourth forward speed stage D4.

In a state that the third rotation shaft TM3 is connected to the seventhrotation shaft TM7 by operation of the first clutch C1, the torque ofthe input shaft IS is input to the second rotation shaft TM2. Inaddition, the sixth and eighth rotation shafts TM6 and TM8 are operatedas the fixed elements by operation of the first and third brakes B1 andB3. Therefore, the torque of the input shaft IS is shifted into thefourth forward speed stage, and the fourth forward speed stage is outputthrough the output shaft OS connected to the seventh rotation shaft TM7.

The first and second clutches C1 and C2 and the first brake B1 areoperated at a fifth forward speed stage D5.

In a state that the third rotation shaft TM3 is connected to the seventhrotation shaft TM7 by operation of the first clutch C1 and the secondrotation shaft TM2 is connected to the sixth rotation shaft TM6 byoperation of the second clutch C2, the torque of the input shaft IS isinput to the second rotation shaft TM2. In addition, the sixth rotationshaft TM6 is operated as the fixed element by operation of the firstbrake B1. Therefore, the torque of the input shaft IS is shifted intothe fifth forward speed stage, and the fifth forward speed stage isoutput through the output shaft OS connected to the seventh rotationshaft TM7.

The first, second, and third clutches C1, C2, and C3 are operated at asixth forward speed stage D6.

In a state that the third rotation shaft TM3 is connected to the seventhrotation shaft TM7 by operation of the first clutch C1, the secondrotation shaft TM2 is connected to the sixth rotation shaft TM6 byoperation of the second clutch C2, and the first rotation shaft TM1 isconnected to the sixth rotation shaft TM6 by operation of the thirdclutch C3, the torque of the input shaft IS is input to the secondrotation shaft TM2. In this case, the first, second, third, and fourthplanetary gear sets PG1, PG2, PG3, and PG4 become lock-up states.Therefore, the torque of the input shaft IS is shifted into the sixthforward speed stage, and the sixth forward speed stage is output throughthe output shaft OS connected to the seventh rotation shaft TM7. At thesixth forward speed stage, the same rotation speed as the input shaft ISis output.

The first and third clutches C1 and C3 and the first brake B1 areoperated at a seventh forward speed stage D7.

In a state that the third rotation shaft TM3 is connected to the seventhrotation shaft TM7 by operation of the first clutch C1 and the firstrotation shaft TM1 is connected to the sixth rotation shaft TM6 byoperation of the third clutch C3, the torque of the input shaft IS isinput to the second rotation shaft TM2. In addition, the sixth rotationshaft TM6 is operated as the fixed element by operation of the firstbrake B1. Therefore, the torque of the input shaft IS is shifted intothe seventh forward speed stage, and the seventh forward speed stage isoutput through the output shaft OS connected to the seventh rotationshaft TM7.

The first and third clutches C1 and C3 and the second brake B2 areoperated at an eighth forward speed stage D8.

In a state that the third rotation shaft TM3 is connected to the seventhrotation shaft TM7 by operation of the first clutch C1 and the firstrotation shaft TM1 is connected to the sixth rotation shaft TM6 byoperation of the third clutch C3, the torque of the input shaft IS isinput to the second rotation shaft TM2. In addition, the fifth rotationshaft TM5 is operated as the fixed element by operation of the secondbrake B2. Therefore, the torque of the input shaft IS is shifted intothe eighth forward speed stage, and the eighth forward speed stage isoutput through the output shaft OS connected to the seventh rotationshaft TM7.

The first clutch C1 and the first and second brakes B1 and B2 areoperated at a ninth forward speed stage D9.

In a state that the first rotation shaft TM1 is connected to the sixthrotation shaft TM6 by operation of the third clutch C3, the torque ofthe input shaft IS is input to the second rotation shaft TM2. Inaddition, the sixth and fifth rotation shafts TM6 and TM5 are operatedas the fixed elements by operation of the first and second brakes B1 andB2. Therefore, the torque of the input shaft IS is shifted into theninth forward speed stage, and the ninth forward speed stage is outputthrough the output shaft OS connected to the seventh rotation shaft TM7.

The first, second, and third brakes B1, B2, and B3 are operated at areverse speed stage REV.

In a state that the torque of the input shaft IS is input to the secondrotation shaft TM2, the sixth, fifth, and eighth rotation shafts TM6,TM5, and TM8 are operated as the fixed elements by operation of thefirst, second, and third brakes B1, B2, and B3. Therefore, the torque ofthe input shaft IS is shifted into the reverse speed stage, and thereverse speed stage is output through the output shaft OS connected tothe seventh rotation shaft TM7.

The planetary gear train according to various embodiments of the presentinvention achieves at least nine forward speed stages and one reversespeed stage by combining four planetary gear sets PG1, PG2, PG3, and PG4with three clutches C1, C2, and C3 and three brakes B1, B2, and B3.

In addition, since gear ratio span greater than 9.4 is secured, drivingefficiency of the engine is maximized.

Furthermore, since linearity of step ratios may be secured due tomultiple speed stages, drivability such as acceleration before and aftershift, rhythmical engine speed, and so on are improved.

For convenience in explanation and accurate definition in the appendedclaims, the terms “upper”, “lower”, “inner” and “outer”, “up,” “down,”“upper”, “lower,” “upwards,” “downwards”, “front”, “rear”, “back”,“inside”, “outside”, “inwardly,” “outwardly,” “interior”, “exterior”,“inner,” “outer”, “forwards” and “backwards” are used to describefeatures of the exemplary embodiments with reference to the positions ofsuch features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A planetary gear train of an automatictransmission for a vehicle including: an input shaft receiving torque ofan engine, an output shaft outputting changed torque of the engine, afirst planetary gear set including a first rotation element, a secondrotation element, and a third rotation element, a second planetary gearset including a fourth rotation element, a fifth rotation element, and asixth rotation element, a third planetary gear set including a seventhrotation element, an eighth rotation element, and a ninth rotationelement, and a fourth planetary gear set including a tenth rotationelement, an eleventh rotation element, and a twelfth rotation element,wherein the input shaft is directly connected to the second rotationelement, the output shaft is directly connected to the eleventh rotationelement, the first rotation element directly connects the sixth rotationelement with the tenth rotation element, the second rotation element isdirectly connected to the fourth rotation element, the fifth rotationelement is directly connected to the ninth rotation element, and theseventh rotation element is selectively connectable to a transmissionhousing.
 2. The planetary gear train of claim 1, wherein the eighthrotation element is selectively connectable to the transmission housing,the twelfth rotation element is selectively connectable to thetransmission housing, the third rotation element is selectivelyconnectable to the eleventh rotation element, the eighth rotationelement is selectively connectable to the input shaft, and the firstrotation element is selectively connectable to the eighth rotationelement.
 3. The planetary gear train of claim 1, wherein the firstrotation element, the second rotation element, and the third rotationelement include a first sun gear, a first planet carrier, and a firstring gear, the fourth rotation element, the fifth rotation element, andthe sixth rotation element include a second sun gear, a second ringgear, and a second planet carrier, the seventh rotation element, theeighth rotation element, and the ninth rotation element include a thirdsun gear, a third planet carrier, and a third ring gear, and the tenthrotation element, the eleventh rotation element, and the twelfthrotation element include a fourth sun gear, a fourth planet carrier, anda fourth ring gear.
 4. A planetary gear train of an automatictransmission for a vehicle including: an input shaft receiving torque ofan engine, an output shaft outputting changed torque of the engine, afirst planetary gear set including a first rotation element, a secondrotation element, and a third rotation element, a second planetary gearset including a fourth rotation element, a fifth rotation element, and asixth rotation element, a third planetary gear set including a seventhrotation element, an eighth rotation element, and a ninth rotationelement, a fourth planetary gear set including a tenth rotation element,an eleventh rotation element, and a twelfth rotation element, a firstrotation shaft directly connecting the first rotation element with thesixth rotation element and the tenth rotation element, a second rotationshaft directly connecting the second rotation element with the fourthrotation element and directly connected to the input shaft, a thirdrotation shaft directly connected to the third rotation element, afourth rotation shaft directly connecting the fifth rotation elementwith the ninth rotation element, a fifth rotation shaft directlyconnected to the seventh rotation element and selectively connectable toa transmission housing, a sixth rotation shaft directly connected to theeighth rotation element, selectively connectable to at least one of thefirst rotation shaft and the second rotation shaft, and selectivelyconnectable to the transmission housing, a seventh rotation shaftdirectly connected to the eleventh rotation element, selectivelyconnectable to the third rotation shaft, and directly connected to theoutput shaft, and an eighth rotation shaft directly connected to thetwelfth rotation element and selectively connectable to the transmissionhousing.
 5. The planetary gear train of claim 4, wherein the firstplanetary gear set is a single pinion planetary gear set, the firstrotation element is a first sun gear, the second rotation element is afirst planet carrier, and the third rotation element is a first ringgear, the second planetary gear set is a double pinion planetary gearset, the fourth rotation element is a second sun gear, the fifthrotation element is a second ring gear, and the sixth rotation elementis a second planet carrier, the third planetary gear set is a singlepinion planetary gear set, the seventh rotation element is a third sungear, the eighth rotation element is a third planet carrier, and theninth rotation element is a third ring gear, and the fourth planetarygear set is a single pinion planetary gear set, the tenth rotationelement is a fourth sun gear, the eleventh rotation element is a fourthplanet carrier, and the twelfth rotation element is a fourth ring gear.6. The planetary gear train of claim 4, further including: a firstclutch selectively connecting the third rotation shaft with the seventhrotation shaft, a second clutch selectively connecting the secondrotation shaft with the sixth rotation shaft, a third clutch selectivelyconnecting the first rotation shaft with the sixth rotation shaft, afirst brake selectively connecting the sixth rotation shaft with thetransmission housing, a second brake selectively connecting the fifthrotation shaft with the transmission housing, and a third brakeselectively connecting the eighth rotation shaft with the transmissionhousing.
 7. The planetary gear train of claim 6, wherein a first forwardspeed stage is achieved by operation of the third clutch and the firstand third brakes, a second forward speed stage is achieved by operationof the second and third clutches and the third brake, a third forwardspeed stage is achieved by operation of the second clutch and the firstand third brakes, a fourth forward speed stage is achieved by operationof the first clutch and the first and third brakes, a fifth forwardspeed stage is achieved by operation of the first clutch and the secondclutch and the first brake, a sixth forward speed stage is achieved byoperation of the first, second, and third clutches, a seventh forwardspeed stage is achieved by operation of the first and third clutches andthe first brake, an eighth forward speed stage is achieved by operationof the first and third clutches and the second brake, a ninth forwardspeed stage is achieved by operation of the first clutch and the firstand second brakes, and a reverse speed stage is achieved by operation ofthe first, second, and third brakes.
 8. A planetary gear train of anautomatic transmission for a vehicle including: an input shaft receivingtorque of an engine, an output shaft outputting changed torque, a firstplanetary gear set including a single pinion planetary gear set andincluding a first rotation element, a second rotation element, and athird rotation element, a second planetary gear set including a doublepinion planetary gear set and including a fourth rotation element, afifth rotation element, and a sixth rotation element, a third planetarygear set including a single pinion planetary gear set and including aseventh rotation element, an eighth rotation element, and a ninthrotation element, a fourth planetary gear set including a single pinionplanetary gear set and including a tenth rotation element, an eleventhrotation element, and a twelfth rotation element, a first rotation shaftdirectly connecting the first rotation element with the sixth rotationelement and the tenth rotation element, a second rotation shaft directlyconnecting the second rotation element with the fourth rotation elementand directly connected to the input shaft, a third rotation shaftdirectly connected to the third rotation element, a fourth rotationshaft directly connecting the fifth rotation element with the ninthrotation element, a fifth rotation shaft directly connected to theseventh rotation element and selectively connectable to a transmissionhousing, a sixth rotation shaft directly connected to the eighthrotation element, selectively connectable to at least one of the firstrotation shaft and the second rotation shaft, and selectivelyconnectable to the transmission housing, a seventh rotation shaftdirectly connected to the eleventh rotation element, selectivelyconnectable to the third rotation shaft, and directly connected to theoutput shaft, an eighth rotation shaft directly connected to the twelfthrotation element and selectively connectable to the transmissionhousing, a first clutch selectively connecting the third rotation shaftwith the seventh rotation shaft, a second clutch selectively connectingthe second rotation shaft with the sixth rotation shaft, a third clutchselectively connecting the first rotation shaft with the sixth rotationshaft, a first brake selectively connecting the sixth rotation shaftwith the transmission housing, a second brake selectively connecting thefifth rotation shaft with the transmission housing, and a third brakeselectively connecting the eighth rotation shaft with the transmissionhousing.
 9. The planetary gear train of claim 8, wherein the firstrotation element, the second rotation element, and the third rotationelement include a first sun gear, a first planet carrier, and a firstring gear, the fourth rotation element, the fifth rotation element, andthe sixth rotation element include a second sun gear, a second ringgear, and a second planet carrier, the seventh rotation element, theeighth rotation element, and the ninth rotation element include a thirdsun gear, a third planet carrier, and a third ring gear, and the tenthrotation element, the eleventh rotation element, and the twelfthrotation element include a fourth sun gear, a fourth planet carrier, anda fourth ring gear.
 10. The planetary gear train of claim 8, wherein afirst forward speed stage is achieved by operation of the third clutchand the first and third brakes, a second forward speed stage is achievedby operation of the second and third clutches and the third brake, athird forward speed stage is achieved by operation of the second clutchand the first and third brakes, a fourth forward speed stage is achievedby operation of the first clutch and the first and third brakes, a fifthforward speed stage is achieved by operation of the first clutch and thesecond clutch and the first brake, a sixth forward speed stage isachieved by operation of the first, second, and third clutches, aseventh forward speed stage is achieved by operation of the first andthird clutches and the first brake, an eighth forward speed stage isachieved by operation of the first and third clutches and the secondbrake, a ninth forward speed stage is achieved by operation of the firstclutch and the first and second brakes, and a reverse speed stage isachieved by operation of the first, second, and third brakes.